The use of supercritical fluid extraction techniques and supercritical fluid chromatography are well known. See, e.g., U.S. Pat. Nos. 4,814,089 and 4,871,453. See generally, Glob Modern Practice of Gas Chromatography, 2d ed., John Wiley & Sons 1985 and Novotry et al. Temperature and Pressure Effects in Supercritical Fluid Chromatography, Journal of Chromatographic Science Jun. 1971.
Supercritical fluid extraction permits the extraction of materials which are difficult to separate. Typically it is used in the extraction of complex, high molecular weight mixtures including polymers. This method utilizes a mobile phase of a highly compressed gas, such as CO.sub.2, at or above its critical temperature and pressure. The physical properties of these gases are between those of gases and liquids which results in a good transport of the analyte.
It is known that the effectiveness of the supercritical fluid extraction is the ability to change the density of the mobile phase which effects solvation, diffusion and viscosity of the fluid.
Notwithstanding the versatility of supercritical fluid extraction, it is very difficult to extract analytes from liquid media such as an aqueous media. See, Thiebaut, D., et al., Journal of Chromatography, "Supercritical-Fluid Extraction of Aqueous Samples And On-Line Coupling To Supercritical-Fluid Chromatography," 477 (1989) 151-159. Using CO.sub.2 as the fluid, up to 0.3% of the water from the aqueous solution is dissolved in the fluid. As the fluid is passed over the sample, water is continuously entrained and the extracted sample results in a two phase system. For this reason, dynamic extractions have not provided the desired result because the sample along with the media is moved from one container to another. Static extractions where the vessel is pressurized for a period of time are inefficient and slow.
Other solutions to this problem have been sought, however, they have only been successful in large scale systems such as in waste water treatment. See, e.g., (1) Kuk, M.S.; Montagna, J.C., Chemical Engineering at Supercritical Fluid Conditions; Paulitis, M.E., Penninger, J.D., Gray R.D., Davison, K.P. Eds.; Ann Arbor Science; Ann Arbor, Mich., 1983; pp. 101-111; (2) Ehntholt, D.J.; Thrun, K.; Eppig, C.; Ringhand, P.J., Environ. Anal. Chem. 1983, 13, 219-235; (3) Eckert, C.A.; Van Alstein, J.G.; Stoicos, T., Environ. Sci. Technol. 1986, 20, 319-325; and (4) Roop, R.K.; Akgerman A.; Irvin, T.R.; Steens, E.K.J., Supercrit. Fluid 1988, 1, 31-36.
Accordingly, an object of the present invention is to provide a method and means for the supercritical fluid extraction of samples in an aqueous media.